The applicant has filed an application for an invention that relates to a seat reclining apparatus which includes a base plate which is fixed to a seat cushion side frame, a ratchet plate (ratchet) which is fixed to a seatback side frame and provided on the inner periphery thereof with an annular internal gear, a rotational center shaft (hand-operated shaft) for the base plate and the ratchet plate, a plurality of lock members (pawls) which are supported on an inner side of the base plate (a surface of the base plate which faces the ratchet plate) thereby to be movable (slidable) relative to the base plate in radial directions of the rotational center shaft, a rotational cam which rotates with the rotational center shaft, and a lock spring (spiral spring) which biases and rotates the rotational center shaft (application number: Japanese patent application No. 2012-86426).
A spring cover for housing the lock spring, in a space formed between an outer surface of the base plate of the seat reclining apparatus and the spring cover, is mounted to the outer surface of the base plate. An exposing hole that constitutes a through-hole is formed in a seat cushion side frame, and the spring cover is exposed toward the outside of the seat cushion side frame through this exposing hole.
An external gear is formed on the outer periphery of each lock member. Each lock member is movable relative to the base plate between an engaged position in which the external gear is engaged with the internal gear of the ratchet plate and a disengaged position in which the external gear is disengaged, toward the inner peripheral side from the internal gear of the ratchet plate.
The rotational cam is rotatable between a locked position to position each lock member in the engaged position, and an unlocked position to position each lock member in the disengaged position. The lock spring biases the rotational center shaft in a direction to rotate the rotational cam toward the locked position.
When an operating lever which is interconnected with the rotational center shaft is not rotationally operated, the rotational cam rotates toward the locked position by the rotational biasing force of the lock spring, which causes each lock member to move toward the engaged position. Accordingly, the outer gear of each lock member is engaged with the internal gear of the ratchet plate, so that the seatback side frame (seatback) becomes nonrotatable relative to the seat cushion side frame (seat cushion).
On the other hand, when the operating lever is operated rotationally against the rotational biasing force of the lock spring, the rotational cam moves to the unlocked position. Thereupon, each lock member, which has been moved to the engaged position, moves toward the disengaged position, which causes the outer gear of each lock member to be disengaged from the internal gear of the ratchet plate. Accordingly, the seatback side frame (seatback) becomes rotatable (the angle of the seatback becomes adjustable) relative to the seat cushion side frame (seat cushion).